As is known in the art, systems are available for determining spatial position and angular orientation, or 6 degrees of freedom, of an object. In other words, these systems determine roll, pitch and yaw, and X, Y and Z position within some arbitrary coordinate system. One such system involves locating three or more fixed points on an object via a position-sensitive detector. The detector records each fixed point's projected two-dimensional location on the detector. Given a priori knowledge of the geometrical arrangement of the fixed points on the object and their projected two-dimensional location on the detector, the system uses mathematical processing to determine position and angular orientation of the object (i.e. six degrees of freedom: x, y, and z positions and pitch, yaw, and roll angular orientations) in space relative to a coordinate system centered at a preselected point in space, typically at a point fixed relative to the detector.
Such systems have many applications. For example, by selecting different points on the landing deck of a ship, a helicopter or plane could measure how the deck was moving and use that information to land automatically.
There are multiple methods for marking fixed points on an object. One such method includes passive retro-reflectors affixed to the object, which reflect optical, radar, or other electromagnetic radiation beamed at the object back to the detector. Another method includes active radiating emitters affixed to the object. There are also multiple position-sensitive detector systems. One such detector system is an imager, such as a digital camera, that divides the imaged space into pixels and determines the two-dimensional location of each point by its pixel location. A second detector system is an analog position-sensitive device that centroids the incoming light and produces a voltage that varies depending on the light's location on the detector.
Prior position and orientation measurement systems and methods suffer several disadvantages. Analog position-sensitive devices centroid all of the light that falls onto them at once, preventing them from identifying all of the fixed points on the object at once. To avoid this, previous systems and methods such as the one described in U.S. Pat. No. 6,266,142 have the fixed points marked with beacons that radiate one at a time. That way, the detector can identify each beacon in turn until all beacons have illuminated the detector. This is a slower approach than locating all fixed points at once, and becomes even slower as additional points are added. In addition, the transmitting beacons and the position-sensitive detector must be synchronized, adding to the system's complexity. Other previous systems and methods, such as the one described in U.S. Pat. No. 4,896,962, use beacons such as light-emitting diodes (LEDs) and a two-dimensional imager such as a digital camera. Locating the beacons in a two-dimensional image requires more computing and processing power than doing the same with analog position-sensitive devices, and the beacons are not uniquely identified.
In view of the foregoing, it is apparent that there is a need for an inexpensive system that will accurately and quickly determine orientation and position of an object, irrespective of whether there is or is not relative movement between a detector and beacons on the object.